Day21 (multidimensional array, Arrays class)

Multidimensional Arrays

A multidimensional array can be regarded as an array of arrays. For example, a two-dimensional array is a special one-dimensional array, each element of which is a one-dimensional array.

Two-dimensional array:

int a[][] = new int[2][5];

Analysis: The above two-dimensional array a can be regarded as an array with two rows and five columns.

Thinking: The use of multidimensional arrays?

public class A0124ArrayDemo01 {
    
    
    public static void main(String[] args) {
    
    
        int[][] a;
        a = new int[3][3];   // int[][] a =new int [3][3];
        a[0][0]=1;
        a[0][1]=3;
        a[0][2]=5;
        a[1][0]=2;
        a[1][1]=4;
        a[1][2]=6;
        a[2][0]=3;
        a[2][1]=6;
        a[2][2]=9;          //int[][] a ={
    
    {1,3,5},{2,4,6},{3,6,9}}
        System.out.println(a[2][2]);
        //打印二维数组中的元素
        for (int i=0;i<a.length;i++)
        {
    
    for(int j=0;j<a[i].length;j++){
    
    
            System.out.print(a[i][j]+"\t");
        }
            System.out.println();}
    }
}

Arrays 类

import java.util.Arrays;
public class A0124Arrays {
    
    

    public static void main(String[] args) {
    
    
        int[] a = {
    
    22,55,666,1,3,546};
        System.out.println(a);
        //Arrays方法 Arrays.toString(a) 打印数组元素
        System.out.println("打印数组元素：\t"+Arrays.toString(a));
        printArrays(a);//自己写的方法
        //数组重新排序,升序
        Arrays.sort(a);  // sort  vt. 将…分类；将…排序；挑选出某物
        System.out.println("打印排序后的数组：\t"+Arrays.toString(a));
        //数组填充
        Arrays.fill(a,0);//不用输入：（val:）
        System.out.println(Arrays.toString(a));
        int[] b = {
    
    22,55,666,1,3,546};
        Arrays.fill(b,1,3,0);//从1开始，在3之前的元素赋值为0
        System.out.println(Arrays.toString(b));
    }
    
    //不建议重复造轮子
    public static void printArrays(int[] a){
    
    
    System.out.print("自己写的方法：\t[");
    for (int i=0;i<a.length-1;i++){
    
    
        System.out.print(a[i]+",");
    }System.out.print(a[a.length-1]+"]");
        System.out.println();}
}
run：
[I@1b6d3586
打印数组元素：	[22, 55, 666, 1, 3, 546]
自己写的方法：	[22,55,666,1,3,546]
打印排序后的数组：	[1, 3, 22, 55, 546, 666]
[0, 0, 0, 0, 0, 0]
[22, 0, 0, 1, 3, 546]

Process finished with exit code 0